This invention relates to the fabrication of microminiature devices and, more particularly, to an x-ray lithographic system utilized to make structures such as large-scale-integrated semiconductor devices.
An advantageous x-ray lithographic system for replicating submicron features on large areas in a highspeed way is described in IEEE Transactions on Electron Devices, Vol. ED-22, No. 7, July 1975, pages 429-433. To prevent the attenuation of x-rays in the exposure chamber of the described system, the chamber is typically either filled with helium or else maintained at a pressure less than about 10.sup.-2 Torr.
In practice, it has been observed that the presence of certain constituents such as oxygen in the mask-to-resist-coated-wafer region of an x-ray lithographic system significantly inhibits the exposure of the resist material to incident x-rays. Such inhibitors can be removed from the specified region by, for example, evacuating the exposure chamber, as mentioned above. But the evacuation process is time-consuming and thereby imposes an undesirable limit on the throughput capabilities of the system.
Moreover, although a helium atmosphere established in the exposure chamber can also be effective in removing inhibitors from the mask-to-wafer region, the cleansing action achieved thereby in practice occurs relatively slowly. Hence a system with a helium-filled exposure chamber also exhibits limited throughput capabilities.
In prior art x-ray lithographic systems as heretofore proposed, the aforementioned atmosphere in the mask-to-wafer region is invariably the same as that maintained in the source-to-mask zone. Accordingly, even aside from considerations of throughput, applicants recognized that such known systems are inherently inflexible and not easily adaptable to having their exposure characteristics optimized under a variety of operating conditions. After recognizing these deficiencies of known systems, applicants directed their efforts at trying to devise an improved x-ray exposure system having advantageous throughput characteristics and at the same time exhibiting the flexibility of being arrangeable to enhance other specified properties of the exposure process carried out in the system.